The Clan's mission is to promote the Clan's heritage in its ancient territories in and around Glenshee, to maintain and develop the Clan's sites of historic interest, and to encourage and support worldwide kinship among its Clansfolk.

The Clan MacThomas Society publicises the surnames linked to the Clan at Scottish events, in articles, through social media and on its website, as well as providing genealogy support to help trace descendants of the Clan, in order to recruit as many members as possible into the Society's worldwide connected network of branches. The Society maintains regular communication with its members through newsletters, a Clan magazine, Facebook and the website and encourages members to hold branch meetings and other social networking activities around the world. There is an international Clan Gathering in Scotland, in the presence of the Chief, every three years.